« ForrigeFortsett »
1.-PHYSICS. \HE total eclipse on October 4 was remarkable on account of its TH
extreme totality. Although the depth to which the moon was immersed in the earth's shadow was less than in 1877, the red light with which the moon was illuminated on that occasion during the whole of the totality, was altogether absent on October 4, and to the naked eye the moon appeared only as a faint star with no discernible outline. It has been suggested that the absence of the red light was due to the earth's atmosphere being specially opaque, on account of suspended solid matter, or for some other cause, and that this opacity may be associated with the sky glows with which we have now become familiar. The measurement at Parsonstown of the heat radiated by the moon, for some time before and after the totality of the eclipse, may lead to interesting results. It appears that after the eclipse the increase of the heat did not keep pace with that of the light, and when the totality commenced the heating effect showed signs of continuing after the disappearance of the light.
Lord Rayleigh, in his presidential address at the meeting of the British Association in Montreal, touched upon an important point. Speaking of the development of the dynamo-machine, Lord Rayleigh said :
"With regard to the main features of the problem, it would almost seem as if the difficulty lay in want of faith. Long: ago it was recognized that electricity derived from chemical action is (on a large scale) too expensive a source of mechanical power, notwithstanding the fact that (as proved by Joule in 1846) the conversion of electrical into mechanical work can be effected with great economy. From this it is an evident consequence that electricity may advantageously be obtained from mechanical power; and one cannot help thinking that if the fact had been borne steadily in mind, the development of the dynamo might have been much more rapid. But discoveries and inventions are apt to appear obvious when regarded from the standpoint of accomplished facts; and I draw attention to the matter only to point the moral that we do well to push the attack persistently when we can be sure beforehand that the obstacles to be overcome are only difficulties of contrivance, and that we are not vainly fighting unawares against a law of Nature.”
In his address, as President of the Mathematical and Physical section of the British Association, Sir William Thomson showed that great progress had been made towards a dynamical theory of everything. He explained how the behaviour of an elastic solid might be imitated by means of rotating fly-wheels with their spindles linked together, and further showed how such a system might be modified, so that “the direction of vibration of waves of rectilinear vibrations propagated through it shall turn round the line of propagation of the waves, just as Faraday's observation proves to be done by the line of
vibration of light in a dense medium between the poles of a powerful magnet.” The vortex theory of matter promises to play an important part in the molecular physics of the future.
At the same meeting of the British Association, Prof. O. J. Lodge suggested a somewhat novel application of high tension electricity. The electricity developed by the old frictional machines, or even by the far more efficient modern machines of Holtz, Voss, and others, has not hitherto been much turned to practical account. Prof. Lodge proposes that large Holtz or Voss machines should be supplied to Atlantic steamers, and driven in foggy weather by their engines, the current generated being discharged from points attached to the masts, in order to clear away the fog. There can be no doubt of the clearance effected by the discharge when the fog is confined to a limited portion of space in the lecture-room. The only practical question at issue is the scale upon which such operations can be conducted.
While the public generally are supposed to be "clamouring " for a universally recognized meridian, there can be no doubt that electricians are in earnest in their desire to obtain a universally recognized unit of power common to them and to the mechanical engineer. It is more than ten years ago that the British Association finally adopted the C.G.S. system of units, a system in which the centimetre, gramme, and second are the fundamental units of length, mass, and time respectively, and all other units are based on these. The dyne is that force which, acting on a gramme for a second, communicates to it a velocity of a centimetre per second ; and the erg is the work done in overcoming a dyne through a centimetre. A magnetic pole of unit strength is one which repels an equal pole at a distance of a centimetre in air with a force of a dyne, and an electric current of unit strength is one which, flowing in a centimetre of wire, bent into a circular arc of a centimetre radius, exerts a force of one dyne on a unit magnetic pole placed at the centre of the circle. The unit of electromotive force is that which does an erg of work in a second in driving the unit of current, and the unit of electric resistance is the resistance of a wire in which a unit current is produced by a unit of electromotive force. Of course, the unit of power is an erg per second, so that a unit current flowing through unit resistance requires unit of power to maintain it.
Now, the dyne is a very small unit of force, being little more than the weight of a milligramme, while the erg is so small that a foot pound is equal to about 13,560,000 ergs. The unit of electric current, however, is somewhat large, being very nearly equal to that which ordinarily flows through a 2,000 candle-power arc-lamp. This being so, it follows that the unit of resistance must be extremely small, or the unit power would not maintain such a current through it-in fact, the unit of resistance is far too small to be of any practical use, or even to admit of material representation. Hence, a resistance equal to 1,000,000,000 C.G.S. units was fixed upon as the practical unit, and a Committee of the British Association was appointed more than twenty years ago to construct a material standard which should represent this resistance.
The Report of this committee, explaining how the standard was determined by a method suggested by Sir Wm. Thomson, and discussing the best material for the construction of permanent standards of resistance belongs to the classics of electricity. The committee did not cease its labours until several standards had been constructed, consisting of coils of wire of various metals and alloys, and the temperatures at which they were found to be correct were carefully registered. The unit of resistance thus determined was called an ohm.
But after twelve or thirteen years it was found that these coils, which originally all possessed the same resistance at their proper temperature, had altered so that no two of them agreed together. It also appeared that errors had crept into the original determination, so that the ohm did not accurately represent 1,000,000,000 units of resistance. Fresh determinations of the ohm were made by several different methods, and conspicuous among these measurements were those of Dr. Joule, Lord Rayleigh, and Professor H. A. Rowland. At the recent conference of electricians at Paris, it was decided to adopt as the standard ohm the resistance of a column of pure mercury one square millimetre in section, and 106 centimetres in length at 0°C. The researches of Lord Rayleigh, indicated that the length should be about 106-25 centimetres, while those of Professor Rowland, not yet published, indicate 106-28 centimetres as the proper length. The whole number, was however, preferred by the conference, and this resistance may be regarded as the starting point for all electrical units.
The unit of current adopted in practice is the ampere, which is onetenth of the C.G.S. unit, above referred to. Hence the electromotive force required to maintain an ampere through the resistance of an ohm is 100,000,000 C.G.S. units, and this electromotive force is called a volt. It differs very little from the electromotive force of an ordinary Daniell's cell.
The work required to maintain a current is the product of the current and the electromotive force required to drive it. Since the ampere is one-tenth of the C.G.S. unit, and the volt is 100,000,000 C.G.S. units, it follows that, when an ampere is driven by a volt, work is done at the rate of 10,000,000 ergs per second. This rate of doing work is called a watt, so that a watt is a quantity of the same kind as horse-power. The power required to drive any electric current is given at once in watts, by multiplying the current expressed in amperes by the electromotive force expressed in volts.
Now one-horse power is equivalent to 7,458,000,000 ergs per second, while the watt is 10,000,000 ergs per second. Hence the horsepower is 745.8 watts, and the rule for finding the horse-power required to maintain a current is to divide the product of the volts and amperes by 746. Arithmetic, however, is becoming daily more unpopular, and it is obvious to electricians that this number ought to be exchanged for some power of 10. Clearly there is only one way to accomplish this—viz., by changing the horse-power, which is already nearly 50 per cent. in excess of the power of ordinary horses. Consequently, at the recent conference of electricians at Philadelphia, it was resolved, on the motion of Mr. W. H. Preece, that it is desirable to raise the horse-power so as to make it equal to 1,000 watts. The new horse-power so defined will be about double the power of an ordinary horse, and will be equal to nearly 44,250 foot-pounds per minute. We have yet to hear what the mechanical engineers have to say to this proposal, as they have by far the greatest vested interest in the old horse-power of James Watt.
But whatever may be thought of the practical suggestions of the conference, the inaugural address of the president, Professor H. A. Rowland, of John Hopkins University, contained many passages worth remembering. Having showed that electricity “is not energy, but is a property of matter and incapable of existing apart from matter," Professor Rowland said :
“The theory of matter then includes electricity and magnetism, and hence light; it includes gravitation, heat, and chemical action; it forms the great problem of the universe. When we know what matter is, then the theories of light and heat will also be perfect, then and only then shall we know what is electricity and what is magnetism. . . . . We have seen how the feeble spirit which was waked up by friction in the amber, and went forth to draw in light bodies, has grown until it now dazzles the world by its brilliancy, and carries our thoughts from one extremity of the world to the other. It is the genius of Aladdin's lamp, which, when thoroughly roused, goes forth into the world to do us service, and returns bearing us wealth, and honour, and riches. But it can never be the servant of an ignorant or lazy world. Like the genius of Aladdin's lamp, it appeared to the world when the amber was rubbed, but the world knew not the language in which to give it orders, and was too lazy to learn it. The spirit of the amber appeared before them to receive its orders, but was only gazed at in silly wonder, and retired in disgust. They had but to order it and it would have gone to the uttermost part of the earth with almost the velocity of light to do their bidding. But in their ignorance they knew not its language. For two thousand years they did not study it, and when they began to do so, it took them two hundred and fifty years to learn the language sufficiently to make a messenger of it. And even now we are but children studying its A B C. It is knowledge —more knowledge, that we want.”
The domains of physics and physiology seem doomed to become more and more intimately associated. By means of a platinum wire passing through a glass tube, and surrounded by dilute sulphuric acid, or solution of zinc sulphate, Professor Hermann succeeded in reproducing many of the electric phenomena of living nerves. The electrodes connected with the battery, which is to stimulate the artificial nerve, as well as those connected with the galvanometer, which is to receive and measure the nerve current, are inserted in the liquid without touching the wire. The action appears to depend on the creeping of a state of polarization along the wire as the polarization opposite the electrodes opposes the passage of the current, and compels it to go out of its way to gain admission to the wire. The current in the galvanometer does not immediately succeed the introduction of the battery current, but it follows it at an interval, increasing with the distance of the galvanometer terminals from those of the battery. During the summer the phenomenon has been carefully investigated by Professor Hermann and Dr. Samways, and the velocity of the wave along the artificial nerve has been measured. It varies with different electrolytes, but in their experiments was always between ten and sixty metres per second, while in the first measurement made it was 283 metres per second. The velocity of the " action current in a frog's nerve was found by Bernstein to vary between 25 and 32 metres per second.
These narratives of fictitious joys and sorrows, which from time to time we are called on to bring before the notice of our readers have an interest in some degree independent of their artistic merit. They mirror the changing thoughts and interests which occupy the mind of large classes of men and women in a way which no other branch of literature can pretend to do. We do not mean that novels show what life is like. We would assure all such very young ladies and gentlemen as may not know it already, that fictitious experience is to real as New York, in the opinion of the traveller in Martin Chuzzlewit," was to Old York; the American reminding him of the English city on account of its being so totally dissimilar in every respect. But novels shed light on the ideas of that large and increasing class who write novels, and on the way in which the larger and faster increasing class who read novels are being taught to think of life. They reflect the changing views of all that is interesting to average humanity, and exhibit on convenient scale the varying aspects of social life, so far as it is revealed in the subjects which writers attempt to represent, and the interests which they try to satisfy, independently of their success in these aims. The fiction of our own day shows us its breach with the past, its distrust of authority, its craving for originality, its abhorrence of privilege, in some respects better than other literature does. The old landmarks we see are being obli. terated, much that was taken for granted but yesterday is questioned, some of it is even denied. The relations of human beings to God, and of men to women, are alike investigated and scanned in a way that would have shocked our fathers.
What a landmark, for instance, in the history of religious thought is such a novel as “We Two."* A saintly Atheist, whose daughter is converted to Christianity by a liberal clergyman, could hardly have been delineated in fiction much before the year 1881. The appositeness of such a conjunction to mark its own date is not impaired by the fact that as a picture of society the account of the persecution to which the Atheist is subjected is obsolete, and the moral which the writer urges unnecessary. When a large constituency chooses to be represented in Parliament by an eminent atheist, even though Parliament makes a difficulty of receiving him (which everybody knows will have to be done sooner or later) ; when it is not uncommon to find oneself in company where a good deal more courage is necessary to profess Christianity than Atheism, a warning against Christian bigotry if it is to be forcible should take a historic form. We should have liked the story made contemporary, say, with the burning of Priestley's house at Birmingham. But this is a mere criticism of detail ; the book is not less accurate as an expression of contemporary feeling, because it is a gross anachronism as a description of contemporary society. It is valuable not only in the description of that influence
* “We Two." By Edna Lyall. London : Hurst & Blackett. 3 vols.